The characteristics of mass spectrometry have raised it to an outstanding position among the various analysis methods. It has excellent sensitivity and detection limits and may be used in a wide variety of applications, e.g. atomic physics, reaction physics, reaction kinetics, geochronology, biomedicine, ion-molecule reactions, and determination of thermodynamic parameters (ΔG°f, Ka, etc.). Mass spectrometry technology has thus begun to progress very rapidly as its uses have become more widely recognized. This has led to the development of entirely new instruments and applications.
One type of mass spectrometer, known as an ion trap mass analyzer, is illustrated in FIG. 1. Ion trap mass analyzers are similar to quadrupole mass analyzers in that RF voltages are applied to produce an oscillating ion trajectory. The term “ion trap” is derived from the fact that the fields are applied so that ions of all mass-to-charge ratios are initially trapped, and oscillate in the mass analyzer. Mass analysis is subsequently accomplished by sequentially applying a mass-to-charge dependent matching RF voltage that increases the amplitude of the oscillations in a manner that ejects ions of increasing mass-to-charge ratio out of the trap and into the detector. This type of operation is referred to as “mass-selective instability” because all ions are retained in the fields of the mass analyzer except those with the selected mass-to-charge ratio.
Development trends in such mass analyzers have gone in the direction of increasingly complex designs requiring highly specialized components and tight manufacturing tolerances. This increased complexity frequently results in undesirable trade-offs in the size, reliability and manufacturability of the apparatus. However, such trade-offs have become increasingly intolerable in the competitive field of drug discovery and analysis. There, mass analyzers must be highly accurate, reliable and, at times, compact in design.
The present inventors have recognized that there is a need to improve existing mass spectrometer apparatus. Such existing mass spectrometer apparatus are frequently of a highly complex design and are difficult to operate. Decreased complexity can be achieved by simplifying the mass spectrometer apparatus and/or simplifying the methods used for ion selection. Such improvements can be achieved while still maintaining or exceeding manufacturing, mass resolution, and/or mass sensitivity goals.